/***************************************************************
*  NAME:  
*	    md5
*  SYNOPSIS:
*    	    implementation of the md5
*  DESCRIPTION:
*     	    
*  HISTORY:
*      	         dietrich - Oct 5, 2011:  Created.
*
***************************************************************/

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <arpa/inet.h>   /* endianness */
#include "digest.h"


/*
 * MD5 
 *
 * 512 bits of input  reduced to 128 bits hash
 * each 512 bits block is hashed independantly.  The hashes
 * are added together. Result is final sum and  may overflow.
 *
 * 64 transformation on each input block.
 * split the input block in 16 32bits chuncks.
 * The current hash in split into 4 32 bits chuncks,referred as A,B,C,D.
 * Most operations are done on A,B,C,D which are added to the input.
 * The 64 ops: consist of the 4 flipping functions F,G,H,I.
 * Operates on little-endian
 *
 * The resulting hash is 128 bit long (16 bytes).
 * MD5 algo is little endian.
 *
 * MD5 vulnerabilities.
 * Birth day paradox. 2.2 10⁹ for 50% chance of a collision.
 * papers page 170.
 */

/*
 * MD5 Flipping functions
 *  F acts as a conditional a conditional in each bit position.
 *  If the bits of x,y,z are independant and unbiased, the resulting bits
 *  are independant and unbiased.
 *  H is a parityu function
 */


/*
 *  hash value endianess 
 */

unsigned int F(unsigned int x, unsigned int y, unsigned int z)
{
  return (x & y) | (~x & z);
}

unsigned int G(unsigned int x, unsigned int y, unsigned int z)
{
  return (x & z) | (y & ~z);
}
unsigned int H(unsigned int x, unsigned int y, unsigned int z)
{
  return (x ^ y ^ z);
}
unsigned int I(unsigned int x, unsigned int y, unsigned int z)
{
  return y ^ (x | ~z);
}

#define BASE_T 4294967296.0


#define S11 7
#define S12 12
#define S13 17
#define S14 22
#define S21 5
#define S22 9
#define S23 14
#define S24 20
#define S31 4
#define S32 11
#define S33 16
#define S34 23
#define S41 6
#define S42 10
#define S43 15
#define S44 21



#define MD5_BLOCK_SIZE   64
#define MD5_INPUT_BLOCK_SIZE 56
#define MD5_RESULT_SIZE   4
#define MD5_RESULT_SIZE  4

void swap_hash(unsigned int hash[MD5_RESULT_SIZE])
{
	int k;

	for(k=0; k<MD5_RESULT_SIZE; k++)
		hash[k] = htonl(hash[k]);
}

void md5_block_operate(const unsigned char *input,
		       unsigned int hash[MD5_RESULT_SIZE])
{
  unsigned int a, b, c, d;
  int j;
  unsigned int x [16];

  swap_hash(hash);

  a = hash[0];
  b = hash[1];
  c = hash[2];
  d = hash[3];

  // input is little endian low bytes of input are first  | i0 | i1 | i2 | i3
  // x = i3 | i2 | i1 | i0
  for (j=0; j<16; j++)
  {
    x [j] = input[(j*4)+3 ] << 24 |
      input[(j*4)+2] << 16 |
      input[(j*4)+1] << 8 |
      input[(j*4) ] ;
  }

  // ROUND 1
  // let [abcd ks i ] denote the operation
  //  a = b + ((a + F(b,c,d) + X[k] +T[i]) <<< s)
  //        <<< = circular rotation left.
  //  T[i 0..64] = int (4294967296 * abs (sin (i) ) )
  
#define ROUND(F, a, b, c, d, k, s, i)  \
  a = ( a + F(b,c,d) + k +  i); \
  a = (a<<s) | (a>>(32-s)); \
  a += b;

#define FF(a,b,c,d,x,s,i)   ROUND(F,a,b,c,d,x,s,i)
#define GG(a,b,c,d,x,s,i)   ROUND(G,a,b,c,d,x,s,i)
#define HH(a,b,c,d,x,s,i)   ROUND(H,a,b,c,d,x,s,i)
#define II(a,b,c,d,x,s,i)   ROUND(I,a,b,c,d,x,s,i)      
  
  /* Round 1 */
  FF (a, b, c, d, x[ 0], S11, 0xd76aa478); /* 1 */
  FF (d, a, b, c, x[ 1], S12, 0xe8c7b756); /* 2 */
  FF (c, d, a, b, x[ 2], S13, 0x242070db); /* 3 */
  FF (b, c, d, a, x[ 3], S14, 0xc1bdceee); /* 4 */
  FF (a, b, c, d, x[ 4], S11, 0xf57c0faf); /* 5 */
  FF (d, a, b, c, x[ 5], S12, 0x4787c62a); /* 6 */
  FF (c, d, a, b, x[ 6], S13, 0xa8304613); /* 7 */
  FF (b, c, d, a, x[ 7], S14, 0xfd469501); /* 8 */
  FF (a, b, c, d, x[ 8], S11, 0x698098d8); /* 9 */
  FF (d, a, b, c, x[ 9], S12, 0x8b44f7af); /* 10 */
  FF (c, d, a, b, x[10], S13, 0xffff5bb1); /* 11 */
  FF (b, c, d, a, x[11], S14, 0x895cd7be); /* 12 */
  FF (a, b, c, d, x[12], S11, 0x6b901122); /* 13 */
  FF (d, a, b, c, x[13], S12, 0xfd987193); /* 14 */
  FF (c, d, a, b, x[14], S13, 0xa679438e); /* 15 */
  FF (b, c, d, a, x[15], S14, 0x49b40821); /* 16 */

 /* Round 2 */
  GG (a, b, c, d, x[ 1], S21, 0xf61e2562); /* 17 */
  GG (d, a, b, c, x[ 6], S22, 0xc040b340); /* 18 */
  GG (c, d, a, b, x[11], S23, 0x265e5a51); /* 19 */
  GG (b, c, d, a, x[ 0], S24, 0xe9b6c7aa); /* 20 */
  GG (a, b, c, d, x[ 5], S21, 0xd62f105d); /* 21 */
  GG (d, a, b, c, x[10], S22,  0x2441453); /* 22 */
  GG (c, d, a, b, x[15], S23, 0xd8a1e681); /* 23 */
  GG (b, c, d, a, x[ 4], S24, 0xe7d3fbc8); /* 24 */
  GG (a, b, c, d, x[ 9], S21, 0x21e1cde6); /* 25 */
  GG (d, a, b, c, x[14], S22, 0xc33707d6); /* 26 */
  GG (c, d, a, b, x[ 3], S23, 0xf4d50d87); /* 27 */
  GG (b, c, d, a, x[ 8], S24, 0x455a14ed); /* 28 */
  GG (a, b, c, d, x[13], S21, 0xa9e3e905); /* 29 */
  GG (d, a, b, c, x[ 2], S22, 0xfcefa3f8); /* 30 */
  GG (c, d, a, b, x[ 7], S23, 0x676f02d9); /* 31 */
  GG (b, c, d, a, x[12], S24, 0x8d2a4c8a); /* 32 */

  /* Round 3 */
  HH (a, b, c, d, x[ 5], S31, 0xfffa3942); /* 33 */
  HH (d, a, b, c, x[ 8], S32, 0x8771f681); /* 34 */
  HH (c, d, a, b, x[11], S33, 0x6d9d6122); /* 35 */
  HH (b, c, d, a, x[14], S34, 0xfde5380c); /* 36 */
  HH (a, b, c, d, x[ 1], S31, 0xa4beea44); /* 37 */
  HH (d, a, b, c, x[ 4], S32, 0x4bdecfa9); /* 38 */
  HH (c, d, a, b, x[ 7], S33, 0xf6bb4b60); /* 39 */
  HH (b, c, d, a, x[10], S34, 0xbebfbc70); /* 40 */
  HH (a, b, c, d, x[13], S31, 0x289b7ec6); /* 41 */
  HH (d, a, b, c, x[ 0], S32, 0xeaa127fa); /* 42 */
  HH (c, d, a, b, x[ 3], S33, 0xd4ef3085); /* 43 */
  HH (b, c, d, a, x[ 6], S34,  0x4881d05); /* 44 */
  HH (a, b, c, d, x[ 9], S31, 0xd9d4d039); /* 45 */
  HH (d, a, b, c, x[12], S32, 0xe6db99e5); /* 46 */
  HH (c, d, a, b, x[15], S33, 0x1fa27cf8); /* 47 */
  HH (b, c, d, a, x[ 2], S34, 0xc4ac5665); /* 48 */

  /* Round 4 */
  II (a, b, c, d, x[ 0], S41, 0xf4292244); /* 49 */
  II (d, a, b, c, x[ 7], S42, 0x432aff97); /* 50 */
  II (c, d, a, b, x[14], S43, 0xab9423a7); /* 51 */
  II (b, c, d, a, x[ 5], S44, 0xfc93a039); /* 52 */
  II (a, b, c, d, x[12], S41, 0x655b59c3); /* 53 */
  II (d, a, b, c, x[ 3], S42, 0x8f0ccc92); /* 54 */
  II (c, d, a, b, x[10], S43, 0xffeff47d); /* 55 */
  II (b, c, d, a, x[ 1], S44, 0x85845dd1); /* 56 */
  II (a, b, c, d, x[ 8], S41, 0x6fa87e4f); /* 57 */
  II (d, a, b, c, x[15], S42, 0xfe2ce6e0); /* 58 */
  II (c, d, a, b, x[ 6], S43, 0xa3014314); /* 59 */
  II (b, c, d, a, x[13], S44, 0x4e0811a1); /* 60 */
  II (a, b, c, d, x[ 4], S41, 0xf7537e82); /* 61 */
  II (d, a, b, c, x[11], S42, 0xbd3af235); /* 62 */
  II (c, d, a, b, x[ 2], S43, 0x2ad7d2bb); /* 63 */
  II (b, c, d, a, x[ 9], S44, 0xeb86d391); /* 64 */

  hash[0] += a;
  hash[1] += b;
  hash[2] += c;
  hash[3] += d;

  swap_hash(hash);
}


unsigned int md5_initial_hash [] =
{
	/* endianness
	  0x67452301,
	  0xefcdab89,
	  0x98badcfe,
	  0x10325476
	*/
	0x01234567,
	0x89abcdef,
	0xfedcba98,
	0x76543210
};



void md5_finalize(unsigned char * padded_block, int length_in_bits)
{
	// append the length for the last block  in Little Endian
	padded_block[MD5_BLOCK_SIZE - 5] = (length_in_bits & 0xFF000000) >> 24;
	padded_block[MD5_BLOCK_SIZE - 6] = (length_in_bits & 0x00FF0000) >> 16;
	padded_block[MD5_BLOCK_SIZE - 7] = (length_in_bits & 0x0000FF00) >>  8;
	padded_block[MD5_BLOCK_SIZE - 8] = (length_in_bits & 0x000000FF);
}



void new_md5_digest(digest_ctx * context)
{
	context->dtype = digest_MD5;
	context->hash_len = 4;
	context->input_len = 0;
	context->block_len = 0;
	context->hash = (unsigned int *) malloc(context->hash_len * sizeof(unsigned int));
	memcpy(context->hash, md5_initial_hash, context->hash_len * sizeof(unsigned int));
	memset(context->block, 0, DIGEST_BLOCK_SIZE);
	context->block_operate = md5_block_operate;
	context->block_finalize = md5_finalize;
        context->new_ctx = new_md5_digest;
}

